[FFmpeg-devel] [PATCH 1/2] mpeg4_unpack_bframes: Avoid allocations and copies of packet structures

[Andreas Rheinhardt]

Andreas Rheinhardt:
> Andreas Rheinhardt:
>> 1. Since bd90a2ec, mpeg4_unpack_bframes caches whole packets instead of
>> just the pointer to the buffer and the buffer's size in order to be able
>> to make use of refcounting to avoid copying of data; this unfortunately
>> introduced copies of packet structures and side data (if existing),
>> although the only fields that are needed are the buffer-related ones
>> (data, size and buf). This can be changed without compromising the
>> advantages of refcounting by storing a reference to the buffer.
>>
>> 2. This change also makes it easy to use only one packet throughout
>> so that an allocation and free of an AVPacket structure per filtered
>> packet can be saved by switching to ff_bsf_get_packet_ref.
>>
>> 3. Furthermore, this commit also fixes a memleak introduced in bd90a2ec:
>> If a stored b_frame with side data was used for a later frame, the side
>> data would leak when the input frame's properties were copied into the
>> output frame.
>>
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
>> ---
>>  libavcodec/mpeg4_unpack_bframes_bsf.c | 77 ++++++++++++---------------
>>  1 file changed, 35 insertions(+), 42 deletions(-)
>>
>> diff --git a/libavcodec/mpeg4_unpack_bframes_bsf.c b/libavcodec/mpeg4_unpack_bframes_bsf.c
>> index 1daf133ce5..382070b423 100644
>> --- a/libavcodec/mpeg4_unpack_bframes_bsf.c
>> +++ b/libavcodec/mpeg4_unpack_bframes_bsf.c
>> @@ -25,7 +25,7 @@
>>  #include "mpeg4video.h"
>>  
>>  typedef struct UnpackBFramesBSFContext {
>> -    AVPacket *b_frame;
>> +    AVBufferRef *b_frame_ref;
>>  } UnpackBFramesBSFContext;
>>  
>>  /* determine the position of the packed marker in the userdata,
>> @@ -56,32 +56,32 @@ static void scan_buffer(const uint8_t *buf, int buf_size,
>>      }
>>  }
>>  
>> -static int mpeg4_unpack_bframes_filter(AVBSFContext *ctx, AVPacket *out)
>> +static int mpeg4_unpack_bframes_filter(AVBSFContext *ctx, AVPacket *pkt)
>>  {
>>      UnpackBFramesBSFContext *s = ctx->priv_data;
>>      int pos_p = -1, nb_vop = 0, pos_vop2 = -1, ret = 0;
>> -    AVPacket *in;
>>  
>> -    ret = ff_bsf_get_packet(ctx, &in);
>> +    ret = ff_bsf_get_packet_ref(ctx, pkt);
>>      if (ret < 0)
>>          return ret;
>>  
>> -    scan_buffer(in->data, in->size, &pos_p, &nb_vop, &pos_vop2);
>> +    scan_buffer(pkt->data, pkt->size, &pos_p, &nb_vop, &pos_vop2);
>>      av_log(ctx, AV_LOG_DEBUG, "Found %d VOP startcode(s) in this packet.\n", nb_vop);
>>  
>>      if (pos_vop2 >= 0) {
>> -        if (s->b_frame->data) {
>> +        if (s->b_frame_ref) {
>>              av_log(ctx, AV_LOG_WARNING,
>>                     "Missing one N-VOP packet, discarding one B-frame.\n");
>> -            av_packet_unref(s->b_frame);
>> +            av_buffer_unref(&s->b_frame_ref);
>>          }
>> -        /* store the packed B-frame in the BSFContext */
>> -        ret = av_packet_ref(s->b_frame, in);
>> -        if (ret < 0) {
>> +        /* store a reference to the packed B-frame's data in the BSFContext */
>> +        s->b_frame_ref = av_buffer_ref(pkt->buf);
>> +        if (!s->b_frame_ref) {
>> +            ret = AVERROR(ENOMEM);
>>              goto fail;
>>          }
>> -        s->b_frame->size -= pos_vop2;
>> -        s->b_frame->data += pos_vop2;
>> +        s->b_frame_ref->data = pkt->data + pos_vop2;
>> +        s->b_frame_ref->size = pkt->size - pos_vop2;
>>      }
>>  
>>      if (nb_vop > 2) {
>> @@ -89,56 +89,49 @@ static int mpeg4_unpack_bframes_filter(AVBSFContext *ctx, AVPacket *out)
>>         "Found %d VOP headers in one packet, only unpacking one.\n", nb_vop);
>>      }
>>  
>> -    if (nb_vop == 1 && s->b_frame->data) {
>> -        /* use frame from BSFContext */
>> -        av_packet_move_ref(out, s->b_frame);
>> +    if (nb_vop == 1 && s->b_frame_ref) {
>> +        AVBufferRef *tmp = pkt->buf;
>>  
>> -        /* use properties from current input packet */
>> -        ret = av_packet_copy_props(out, in);
>> -        if (ret < 0) {
>> -            goto fail;
>> -        }
>> +        /* make tmp accurately reflect the packet's data */
>> +        tmp->data = pkt->data;
>> +        tmp->size = pkt->size;
>> +
>> +        /* replace data in packet with stored data */
>> +        pkt->buf  = s->b_frame_ref;
>> +        pkt->data = s->b_frame_ref->data;
>> +        pkt->size = s->b_frame_ref->size;
>> +
>> +        /* store reference to data into BSFContext */
>> +        s->b_frame_ref = tmp;
>>  
>> -        if (in->size <= MAX_NVOP_SIZE) {
>> -            /* N-VOP */
>> +        if (s->b_frame_ref->size <= MAX_NVOP_SIZE) {
>> +            /* N-VOP - discard stored data */
>>              av_log(ctx, AV_LOG_DEBUG, "Skipping N-VOP.\n");
>> -        } else {
>> -            /* copy packet into BSFContext */
>> -            av_packet_move_ref(s->b_frame, in);
>> +            av_buffer_unref(&s->b_frame_ref);
>>          }
>>      } else if (nb_vop >= 2) {
>>          /* use first frame of the packet */
>> -        av_packet_move_ref(out, in);
>> -        out->size = pos_vop2;
>> +        pkt->size = pos_vop2;
>>      } else if (pos_p >= 0) {
>> -        ret = av_packet_make_writable(in);
>> +        ret = av_packet_make_writable(pkt);
>>          if (ret < 0)
>>              goto fail;
>>          av_log(ctx, AV_LOG_DEBUG, "Updating DivX userdata (remove trailing 'p').\n");
>> -        av_packet_move_ref(out, in);
>>          /* remove 'p' (packed) from the end of the (DivX) userdata string */
>> -        out->data[pos_p] = '\0';
>> +        pkt->data[pos_p] = '\0';
>>      } else {
>> -        /* copy packet */
>> -        av_packet_move_ref(out, in);
>> +        /* use packet as is */
>>      }
>>  
>>  fail:
>>      if (ret < 0)
>> -        av_packet_unref(out);
>> -    av_packet_free(&in);
>> +        av_packet_unref(pkt);
>>  
>>      return ret;
>>  }
>>  
>>  static int mpeg4_unpack_bframes_init(AVBSFContext *ctx)
>>  {
>> -    UnpackBFramesBSFContext *s = ctx->priv_data;
>> -
>> -    s->b_frame = av_packet_alloc();
>> -    if (!s->b_frame)
>> -        return AVERROR(ENOMEM);
>> -
>>      if (ctx->par_in->extradata) {
>>          int pos_p_ext = -1;
>>          scan_buffer(ctx->par_in->extradata, ctx->par_in->extradata_size, &pos_p_ext, NULL, NULL);
>> @@ -155,13 +148,13 @@ static int mpeg4_unpack_bframes_init(AVBSFContext *ctx)
>>  static void mpeg4_unpack_bframes_flush(AVBSFContext *bsfc)
>>  {
>>      UnpackBFramesBSFContext *ctx = bsfc->priv_data;
>> -    av_packet_unref(ctx->b_frame);
>> +    av_buffer_unref(&ctx->b_frame_ref);
>>  }
>>  
>>  static void mpeg4_unpack_bframes_close(AVBSFContext *bsfc)
>>  {
>>      UnpackBFramesBSFContext *ctx = bsfc->priv_data;
>> -    av_packet_free(&ctx->b_frame);
>> +    av_buffer_unref(&ctx->b_frame_ref);
>>  }
>>  
>>  static const enum AVCodecID codec_ids[] = {
>>
> Ping.
> 
> - Andreas
> 
Another ping.

- Andreas