| Message ID | 20180711215325.84466-1-ottoka@posteo.de |
|---|---|
| State | Superseded |
| Headers | show |
On Wed, Jul 11, 2018 at 11:53:25PM +0200, Karsten Otto wrote: > MP3 frames may not be aligned to aa chunk boundaries. When seeking, > calculate the expected frame offset in the target chunk. Adjust the > timestamp and truncate the next packet accordingly. > > This solution works for the majority of tested audio material. For > some rare encodings with mp3 padding or embedded id3 tags, it will > mispredict the correct offset, and at worst skip an extra frame. > --- > libavformat/aadec.c | 17 ++++++++++++++--- > 1 file changed, 14 insertions(+), 3 deletions(-) > > diff --git a/libavformat/aadec.c b/libavformat/aadec.c > index 17ad20686b..2d78def6e8 100644 > --- a/libavformat/aadec.c > +++ b/libavformat/aadec.c > @@ -37,6 +37,7 @@ > #define TEA_BLOCK_SIZE 8 > #define CHAPTER_HEADER_SIZE 8 > #define TIMEPREC 1000 > +#define MP3_FRAME_SIZE 104 > > typedef struct AADemuxContext { > AVClass *class; > @@ -50,6 +51,7 @@ typedef struct AADemuxContext { > int64_t current_chapter_size; > int64_t content_start; > int64_t content_end; > + int seek_offset; > } AADemuxContext; > > static int get_second_size(char *codec_name) > @@ -228,6 +230,7 @@ static int aa_read_header(AVFormatContext *s) > ff_update_cur_dts(s, st, 0); > avio_seek(pb, start, SEEK_SET); > c->current_chapter_size = 0; > + c->seek_offset = 0; > > return 0; > } > @@ -266,6 +269,8 @@ static int aa_read_packet(AVFormatContext *s, AVPacket *pkt) > // is this the last block in this chapter? > if (c->current_chapter_size / c->current_codec_second_size == 0) { > c->current_codec_second_size = c->current_chapter_size % c->current_codec_second_size; > + if (c->seek_offset > c->current_codec_second_size) > + c->seek_offset = 0; > } > > // decrypt c->current_codec_second_size bytes > @@ -293,12 +298,13 @@ static int aa_read_packet(AVFormatContext *s, AVPacket *pkt) > if (c->current_chapter_size <= 0) > c->current_chapter_size = 0; > > - ret = av_new_packet(pkt, written); > + ret = av_new_packet(pkt, written - c->seek_offset); Please document how the existing checks gurantee that written >= c->seek_offset thanks
diff --git a/libavformat/aadec.c b/libavformat/aadec.c index 17ad20686b..2d78def6e8 100644 --- a/libavformat/aadec.c +++ b/libavformat/aadec.c @@ -37,6 +37,7 @@ #define TEA_BLOCK_SIZE 8 #define CHAPTER_HEADER_SIZE 8 #define TIMEPREC 1000 +#define MP3_FRAME_SIZE 104 typedef struct AADemuxContext { AVClass *class; @@ -50,6 +51,7 @@ typedef struct AADemuxContext { int64_t current_chapter_size; int64_t content_start; int64_t content_end; + int seek_offset; } AADemuxContext; static int get_second_size(char *codec_name) @@ -228,6 +230,7 @@ static int aa_read_header(AVFormatContext *s) ff_update_cur_dts(s, st, 0); avio_seek(pb, start, SEEK_SET); c->current_chapter_size = 0; + c->seek_offset = 0; return 0; } @@ -266,6 +269,8 @@ static int aa_read_packet(AVFormatContext *s, AVPacket *pkt) // is this the last block in this chapter? if (c->current_chapter_size / c->current_codec_second_size == 0) { c->current_codec_second_size = c->current_chapter_size % c->current_codec_second_size; + if (c->seek_offset > c->current_codec_second_size) + c->seek_offset = 0; } // decrypt c->current_codec_second_size bytes @@ -293,12 +298,13 @@ static int aa_read_packet(AVFormatContext *s, AVPacket *pkt) if (c->current_chapter_size <= 0) c->current_chapter_size = 0; - ret = av_new_packet(pkt, written); + ret = av_new_packet(pkt, written - c->seek_offset); if (ret < 0) return ret; - memcpy(pkt->data, buf, written); + memcpy(pkt->data, buf + c->seek_offset, written - c->seek_offset); pkt->pos = pos; + c->seek_offset = 0; return 0; } @@ -342,7 +348,12 @@ static int aa_read_seek(AVFormatContext *s, c->current_chapter_size = chapter_size - chapter_pos; c->chapter_idx = 1 + chapter_idx; - ff_update_cur_dts(s, s->streams[0], ch->start + chapter_pos * TIMEPREC); + // handle extra offset for unaligned frames + if (s->streams[0]->codecpar->codec_id == AV_CODEC_ID_MP3) { + c->seek_offset = (MP3_FRAME_SIZE - chapter_pos % MP3_FRAME_SIZE) % MP3_FRAME_SIZE; + } + + ff_update_cur_dts(s, s->streams[0], ch->start + (chapter_pos + c->seek_offset) * TIMEPREC); return 1; }