ffmpeg軟解碼遇到的坑
內存方面
- 常常碰到解碼過程當中，野指針崩潰。尤爲是當一幀解碼失敗時候。
- ffmepg有引用計數內存管理機制，對應_unref方法。
- 使用結束以後，儘可能使用_unref方法釋放內存，而避免直接_free
int av_packet_ref(AVPacket *dst, const AVPacket *src);
void av_packet_unref(AVPacket *pkt);
複製代碼
解碼器碰到No start code is found.錯誤
[h264 @ 0x7fa318076e00] No start code is found.
[h264 @ 0x7fa318076e00] Error splitting the input into NAL units.
複製代碼
google以後，說沒有使用下列方法bash
/**
* Fill the codec context based on the values from the supplied codec
* parameters. Any allocated fields in codec that have a corresponding field in
* par are freed and replaced with duplicates of the corresponding field in par.
* Fields in codec that do not have a counterpart in par are not touched.
*
* @return >= 0 on success, a negative AVERROR code on failure.
*/
int avcodec_parameters_to_context(AVCodecContext *codec,
const AVCodecParameters *par);
複製代碼
也就是說AVCodecContext有些值沒有設置，致使解碼失敗。幾經嘗試以後，發現有兩個屬性是必要的。ide
uint8_t *extradata;
int extradata_size;
複製代碼
除非是本身編碼的裸數據，mp四、flv等視頻文件解封裝以後，都會有該屬性，對於後續解碼頗有必要。函數
static int h264_decode_frame(AVCodecContext *avctx, void *data,
int *got_frame, AVPacket *avpkt)
{
const uint8_t *buf = avpkt->data;
int buf_size = avpkt->size;
H264Context *h = avctx->priv_data;
AVFrame *pict = data;
int buf_index;
int ret;
h->flags = avctx->flags;
h->setup_finished = 0;
h->nb_slice_ctx_queued = 0;
ff_h264_unref_picture(h, &h->last_pic_for_ec);
/* end of stream, output what is still in the buffers */
if (buf_size == 0)
return send_next_delayed_frame(h, pict, got_frame, 0);
if (h->is_avc && av_packet_get_side_data(avpkt, AV_PKT_DATA_NEW_EXTRADATA, NULL)) {
int side_size;
uint8_t *side = av_packet_get_side_data(avpkt, AV_PKT_DATA_NEW_EXTRADATA, &side_size);
if (is_extra(side, side_size))
ff_h264_decode_extradata(side, side_size,
&h->ps, &h->is_avc, &h->nal_length_size,
avctx->err_recognition, avctx);
}
if(h->is_avc && buf_size >= 9 && buf[0]==1 && buf[2]==0 && (buf[4]&0xFC)==0xFC && (buf[5]&0x1F) && buf[8]==0x67){
if (is_extra(buf, buf_size))
return ff_h264_decode_extradata(buf, buf_size,
&h->ps, &h->is_avc, &h->nal_length_size,
avctx->err_recognition, avctx);
}
buf_index = decode_nal_units(h, buf, buf_size);
if (buf_index < 0)
return AVERROR_INVALIDDATA;
if (!h->cur_pic_ptr && h->nal_unit_type == H264_NAL_END_SEQUENCE) {
av_assert0(buf_index <= buf_size);
return send_next_delayed_frame(h, pict, got_frame, buf_index);
}
if (!(avctx->flags2 & AV_CODEC_FLAG2_CHUNKS) && (!h->cur_pic_ptr || !h->has_slice)) {
if (avctx->skip_frame >= AVDISCARD_NONREF ||
buf_size >= 4 && !memcmp("Q264", buf, 4))
return buf_size;
av_log(avctx, AV_LOG_ERROR, "no frame!\n");
return AVERROR_INVALIDDATA;
}
if (!(avctx->flags2 & AV_CODEC_FLAG2_CHUNKS) ||
(h->mb_y >= h->mb_height && h->mb_height)) {
if ((ret = ff_h264_field_end(h, &h->slice_ctx[0], 0)) < 0)
return ret;
/* Wait for second field. */
if (h->next_output_pic) {
ret = finalize_frame(h, pict, h->next_output_pic, got_frame);
if (ret < 0)
return ret;
}
}
av_assert0(pict->buf[0] || !*got_frame);
ff_h264_unref_picture(h, &h->last_pic_for_ec);
return get_consumed_bytes(buf_index, buf_size);
}
複製代碼
上述代碼位於libcodec/h264dec.c下，是H.264核心的解碼函數，能夠看到，某些狀況下在decode_nal_units() 獲取NAL單元以前，先調用了ff_h264_decode_extradata()來處理extradata數據。主要功能是獲取sps、pps、ps數據，位於libcodec/h264_parse.c下. avccui
int ff_h264_decode_extradata(const uint8_t *data, int size, H264ParamSets *ps,
int *is_avc, int *nal_length_size,
int err_recognition, void *logctx)
{
int ret;
if (!data || size <= 0)
return -1;
if (data[0] == 1) {
int i, cnt, nalsize;
const uint8_t *p = data;
*is_avc = 1;
if (size < 7) {
av_log(logctx, AV_LOG_ERROR, "avcC %d too short\n", size);
return AVERROR_INVALIDDATA;
}
// Decode sps from avcC
cnt = *(p + 5) & 0x1f; // Number of sps
p += 6;
for (i = 0; i < cnt; i++) {
nalsize = AV_RB16(p) + 2;
if (nalsize > size - (p - data))
return AVERROR_INVALIDDATA;
ret = decode_extradata_ps_mp4(p, nalsize, ps, err_recognition, logctx);
if (ret < 0) {
av_log(logctx, AV_LOG_ERROR,
"Decoding sps %d from avcC failed\n", i);
return ret;
}
p += nalsize;
}
// Decode pps from avcC
cnt = *(p++); // Number of pps
for (i = 0; i < cnt; i++) {
nalsize = AV_RB16(p) + 2;
if (nalsize > size - (p - data))
return AVERROR_INVALIDDATA;
ret = decode_extradata_ps_mp4(p, nalsize, ps, err_recognition, logctx);
if (ret < 0) {
av_log(logctx, AV_LOG_ERROR,
"Decoding pps %d from avcC failed\n", i);
return ret;
}
p += nalsize;
}
// Store right nal length size that will be used to parse all other nals
*nal_length_size = (data[4] & 0x03) + 1;
} else {
*is_avc = 0;
ret = decode_extradata_ps(data, size, ps, 0, logctx);
if (ret < 0)
return ret;
}
return size;
}
複製代碼
static int decode_extradata_ps(const uint8_t *data, int size, H264ParamSets *ps,
int is_avc, void *logctx)
{
H2645Packet pkt = { 0 };
int i, ret = 0;
ret = ff_h2645_packet_split(&pkt, data, size, logctx, is_avc, 2, AV_CODEC_ID_H264, 1);
if (ret < 0) {
ret = 0;
goto fail;
}
for (i = 0; i < pkt.nb_nals; i++) {
H2645NAL *nal = &pkt.nals[i];
switch (nal->type) {
case H264_NAL_SPS:
ret = ff_h264_decode_seq_parameter_set(&nal->gb, logctx, ps, 0);
if (ret < 0)
goto fail;
break;
case H264_NAL_PPS:
ret = ff_h264_decode_picture_parameter_set(&nal->gb, logctx, ps,
nal->size_bits);
if (ret < 0)
goto fail;
break;
default:
av_log(logctx, AV_LOG_VERBOSE, "Ignoring NAL type %d in extradata\n",
nal->type);
break;
}
}
fail:
ff_h2645_packet_uninit(&pkt);
return ret;
}
複製代碼
ff_h2645_packet_split()位於libcodec/h2645_parse.c下google
int ff_h2645_packet_split(H2645Packet *pkt, const uint8_t *buf, int length,
void *logctx, int is_nalff, int nal_length_size,
enum AVCodecID codec_id, int small_padding)
{
GetByteContext bc;
int consumed, ret = 0;
int next_avc = is_nalff ? 0 : length;
int64_t padding = small_padding ? 0 : MAX_MBPAIR_SIZE;
bytestream2_init(&bc, buf, length);
av_fast_padded_malloc(&pkt->rbsp.rbsp_buffer, &pkt->rbsp.rbsp_buffer_alloc_size, length + padding);
if (!pkt->rbsp.rbsp_buffer)
return AVERROR(ENOMEM);
pkt->rbsp.rbsp_buffer_size = 0;
pkt->nb_nals = 0;
while (bytestream2_get_bytes_left(&bc) >= 4) {
H2645NAL *nal;
int extract_length = 0;
int skip_trailing_zeros = 1;
if (bytestream2_tell(&bc) == next_avc) {
int i = 0;
extract_length = get_nalsize(nal_length_size,
bc.buffer, bytestream2_get_bytes_left(&bc), &i, logctx);
if (extract_length < 0)
return extract_length;
bytestream2_skip(&bc, nal_length_size);
next_avc = bytestream2_tell(&bc) + extract_length;
} else {
int buf_index;
if (bytestream2_tell(&bc) > next_avc)
av_log(logctx, AV_LOG_WARNING, "Exceeded next NALFF position, re-syncing.\n");
/* search start code */
buf_index = find_next_start_code(bc.buffer, buf + next_avc);
bytestream2_skip(&bc, buf_index);
if (!bytestream2_get_bytes_left(&bc)) {
if (pkt->nb_nals > 0) {
// No more start codes: we discarded some irrelevant
// bytes at the end of the packet.
return 0;
} else {
av_log(logctx, AV_LOG_ERROR, "No start code is found.\n");
return AVERROR_INVALIDDATA;
}
}
extract_length = FFMIN(bytestream2_get_bytes_left(&bc), next_avc - bytestream2_tell(&bc));
if (bytestream2_tell(&bc) >= next_avc) {
/* skip to the start of the next NAL */
bytestream2_skip(&bc, next_avc - bytestream2_tell(&bc));
continue;
}
}
if (pkt->nals_allocated < pkt->nb_nals + 1) {
int new_size = pkt->nals_allocated + 1;
void *tmp = av_realloc_array(pkt->nals, new_size, sizeof(*pkt->nals));
if (!tmp)
return AVERROR(ENOMEM);
pkt->nals = tmp;
memset(pkt->nals + pkt->nals_allocated, 0,
(new_size - pkt->nals_allocated) * sizeof(*pkt->nals));
nal = &pkt->nals[pkt->nb_nals];
nal->skipped_bytes_pos_size = 1024; // initial buffer size
nal->skipped_bytes_pos = av_malloc_array(nal->skipped_bytes_pos_size, sizeof(*nal->skipped_bytes_pos));
if (!nal->skipped_bytes_pos)
return AVERROR(ENOMEM);
pkt->nals_allocated = new_size;
}
nal = &pkt->nals[pkt->nb_nals];
consumed = ff_h2645_extract_rbsp(bc.buffer, extract_length, &pkt->rbsp, nal, small_padding);
if (consumed < 0)
return consumed;
if (is_nalff && (extract_length != consumed) && extract_length)
av_log(logctx, AV_LOG_DEBUG,
"NALFF: Consumed only %d bytes instead of %d\n",
consumed, extract_length);
pkt->nb_nals++;
bytestream2_skip(&bc, consumed);
/* see commit 3566042a0 */
if (bytestream2_get_bytes_left(&bc) >= 4 &&
bytestream2_peek_be32(&bc) == 0x000001E0)
skip_trailing_zeros = 0;
nal->size_bits = get_bit_length(nal, skip_trailing_zeros);
ret = init_get_bits(&nal->gb, nal->data, nal->size_bits);
if (ret < 0)
return ret;
if (codec_id == AV_CODEC_ID_HEVC)
ret = hevc_parse_nal_header(nal, logctx);
else
ret = h264_parse_nal_header(nal, logctx);
if (ret <= 0 || nal->size <= 0) {
if (ret < 0) {
av_log(logctx, AV_LOG_ERROR, "Invalid NAL unit %d, skipping.\n",
nal->type);
}
pkt->nb_nals--;
}
}
return 0;
}
複製代碼
BOX TYPE avcc
0x61 0x76 0x63 0x43
複製代碼
對於mp4文件，如下是avcc具體數據，也就是extradata內容。編碼
0x1 version
0x4d sps[1]
0x40 sps[2]
0x1e sps[3]
0b111111 6位reserved
0b11 2位h264中NALU長度，1+(size&3) = 4
0b111. 3位reserved
0b00001 sps個數1
sps 數據長度23
0x0 0x17
sps長度
0x67 0x4d 0x40 0x1e 0xe8 0x80 0x50 0x8 0x34 0x20 0x0 0x0 0x3 0x0 0x20 0x0 0x0 0x6 0x51 0xe2 0xc5 0xa2 0x40
0x1 pps個數
0x0 0x5 pps長度
pps數據
0x68 0xeb 0xec 0x4c 0x80複製代碼
相關文章
- 1. mac安裝ffmpeg遇到的坑
- 2. ffmpeg開發av_seek_frame遇到的坑
- 3. pycharm軟件遇到的一些坑
- 4. ffmpeg遇到inttypes.h找不到
- 5. mpvue遇到的坑
- 6. finally遇到的坑
- 7. vue遇到的坑
- 8. CodeIgniter遇到的坑
- 9. cocos2dx遇到的坑
- 10. html2canvas遇到的坑
- 更多相關文章...
- • XSL-FO 軟件 - XSL-FO 教程
- • XML 編碼 - XML 教程
- • Scala 中文亂碼解決
- • 常用的分佈式事務解決方案
相關標籤/搜索
每日一句
-
每一个你不满意的现在，都有一个你没有努力的曾经。
最新文章
- 1. python的安裝和Hello，World編寫
- 2. 重磅解讀：K8s Cluster Autoscaler模塊及對應華爲雲插件Deep Dive
- 3. 鴻蒙學習筆記2（永不斷更）
- 4. static關鍵字 和構造代碼塊
- 5. JVM筆記
- 6. 無法啓動 C/C++ 語言服務器。IntelliSense 功能將被禁用。錯誤: Missing binary at c:\Users\MSI-NB\.vscode\extensions\ms-vsc
- 7. 【Hive】Hive返回碼狀態含義
- 8. Java樹形結構遞歸（以時間換空間）和非遞歸（以空間換時間）
- 9. 數據預處理---缺失值
- 10. 都要2021年了，現代C++有什麼值得我們學習的？
歡迎關注本站公眾號,獲取更多信息
相關文章
- 1. mac安裝ffmpeg遇到的坑
- 2. ffmpeg開發av_seek_frame遇到的坑
- 3. pycharm軟件遇到的一些坑
- 4. ffmpeg遇到inttypes.h找不到
- 5. mpvue遇到的坑
- 6. finally遇到的坑
- 7. vue遇到的坑
- 8. CodeIgniter遇到的坑
- 9. cocos2dx遇到的坑
- 10. html2canvas遇到的坑